Coronary heart disease, including acute myocardial infarction (AMI), is the leading cause of death in the United States. ST-elevation myocardial infarction (STEMI) is a common and particularly severe form of AMI for which timely access to percutaneous coronary intervention (PCI) is essential to good patient outcomes. In an attempt to improve outcomes for STEMI patients, STEMI regionalization systems have been established at the local and state level across the United States to quickly route or transfer STEMI patients to a hospital with PCI capability. However, no studies of this relatively new healthcare system have been able to show if, and how, regionalization has improved access and mortality at the community level, as prior work has been limited by studies done in single-hospital settings, the evaluation of only certain process outcomes, and the lack of inclusion of a control group to account for secular trends in improved mortality. Our goals in this proposal are 3-fold: (1) to determine to what extent regionalized STEMI systems are associated with improvements in both access and outcomes, (2) whether vulnerable communities benefit equally within the same system, and (3) how distance and time differentially affect these outcomes. To accomplish these goals, we propose an innovative and definitive approach to study California, a state that provides a natural experiment of STEMI regionalization, as 59% of its counties have regionalized at different times over the study period. We will use a difference-in-differences approach and link non-public patient discharge data from the California Office of Statewide Health Planning and Development between 2006-2011 (H182,800 STEMI patients) with a database designed by the PI of the regionalization status of each county over the same period. In Aim 1, we will determine the extent to which overall access (defined by admission to PCI-capable hospital), treatment (receipt of PCI), and health outcomes differ for STEMI patients in regionalized vs. non-regionalized communities. We hypothesize that the change in probability of being admitted to a PCI- equipped hospital and of receiving PCI will be appreciably higher in counties experiencing regionalization than non-regionalized counties and that health outcomes will improve. In Aim 2, we will determine the extent to which disparities in access, treatment, and outcomes have changed for STEMI patients in regionalized vs. non- regionalized communities. We hypothesize that STEMI patients who belong to traditionally underserved populations will have larger improvements in these metrics post-regionalization relative to the reference population. In Aim 3, we will determine the extent to which changes in access, treatment, and outcome differ for STEMI patients according to distance and time horizon following regionalization. We hypothesize that STEMI patients living farther away from regional PCI centers will benefit differentially more than those living closer to regional PCI centers and benefits of regionalization may not be seen until 1-2 years post- implementation.